/*
 *    This program is free software; you can redistribute it and/or modify
 *    it under the terms of the GNU General Public License as published by
 *    the Free Software Foundation; either version 2 of the License, or
 *    (at your option) any later version.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU General Public License for more details.
 *
 *    You should have received a copy of the GNU General Public License
 *    along with this program; if not, write to the Free Software
 *    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*
 *    SerializedInstancesLoader.java
 *    Copyright (C) 2002 University of Waikato, Hamilton, New Zealand
 *
 */

package weka.core.converters;

import weka.core.Instance;
import weka.core.Instances;
import weka.core.RevisionUtils;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;

/**
 * <!-- globalinfo-start --> Reads a source that contains serialized Instances.
 * <p/>
 * <!-- globalinfo-end -->
 * 
 * @author <a href="mailto:len@reeltwo.com">Len Trigg</a>
 * @version $Revision: 1.15 $
 * @see Loader
 */
public class SerializedInstancesLoader extends AbstractFileLoader implements
		BatchConverter, IncrementalConverter {

	/** for serialization */
	static final long serialVersionUID = 2391085836269030715L;

	/** the file extension */
	public static String FILE_EXTENSION = Instances.SERIALIZED_OBJ_FILE_EXTENSION;

	/** Holds the structure (header) of the data set. */
	protected Instances m_Dataset = null;

	/** The current index position for incremental reading */
	protected int m_IncrementalIndex = 0;

	/**
	 * Returns a string describing this object
	 * 
	 * @return a description of the classifier suitable for displaying in the
	 *         explorer/experimenter gui
	 */
	public String globalInfo() {
		return "Reads a source that contains serialized Instances.";
	}

	/** Resets the Loader ready to read a new data set */
	public void reset() {

		m_Dataset = null;
		m_IncrementalIndex = 0;
	}

	/**
	 * Get the file extension used for arff files
	 * 
	 * @return the file extension
	 */
	public String getFileExtension() {
		return FILE_EXTENSION;
	}

	/**
	 * Gets all the file extensions used for this type of file
	 * 
	 * @return the file extensions
	 */
	public String[] getFileExtensions() {
		return new String[] { getFileExtension() };
	}

	/**
	 * Returns a description of the file type.
	 * 
	 * @return a short file description
	 */
	public String getFileDescription() {
		return "Binary serialized instances";
	}

	/**
	 * Resets the Loader object and sets the source of the data set to be the
	 * supplied InputStream.
	 * 
	 * @param in
	 *            the source InputStream.
	 * @throws IOException
	 *             if there is a problem with IO
	 */
	public void setSource(InputStream in) throws IOException {

		ObjectInputStream oi = new ObjectInputStream(
				new BufferedInputStream(in));
		try {
			m_Dataset = (Instances) oi.readObject();
		} catch (ClassNotFoundException ex) {
			throw new IOException(
					"Could not deserialize instances from this source.");
		}

		// close the stream
		oi.close();
	}

	/**
	 * Determines and returns (if possible) the structure (internally the
	 * header) of the data set as an empty set of instances.
	 * 
	 * @return the structure of the data set as an empty set of Instances
	 * @throws IOException
	 *             if an error occurs
	 */
	public Instances getStructure() throws IOException {

		if (m_Dataset == null) {
			throw new IOException("No source has been specified");
		}

		// We could cache a structure-only if getStructure is likely to be
		// called
		// many times.
		return new Instances(m_Dataset, 0);
	}

	/**
	 * Return the full data set. If the structure hasn't yet been determined by
	 * a call to getStructure then method should do so before processing the
	 * rest of the data set.
	 * 
	 * @return the structure of the data set as an empty set of Instances
	 * @throws IOException
	 *             if there is no source or parsing fails
	 */
	public Instances getDataSet() throws IOException {

		if (m_Dataset == null) {
			throw new IOException("No source has been specified");
		}

		return m_Dataset;
	}

	/**
	 * Read the data set incrementally---get the next instance in the data set
	 * or returns null if there are no more instances to get. If the structure
	 * hasn't yet been determined by a call to getStructure then method should
	 * do so before returning the next instance in the data set.
	 * 
	 * @param structure
	 *            ignored
	 * @return the next instance in the data set as an Instance object or null
	 *         if there are no more instances to be read
	 * @throws IOException
	 *             if there is an error during parsing
	 */
	public Instance getNextInstance(Instances structure) throws IOException {

		if (m_Dataset == null) {
			throw new IOException("No source has been specified");
		}

		// We have to fake this method, since we can only deserialize an entire
		// dataset at a time.
		if (m_IncrementalIndex == m_Dataset.numInstances()) {
			return null;
		}

		return m_Dataset.instance(m_IncrementalIndex++);
	}

	/**
	 * Returns the revision string.
	 * 
	 * @return the revision
	 */
	public String getRevision() {
		return RevisionUtils.extract("$Revision: 1.15 $");
	}

	/**
	 * Main method.
	 * 
	 * @param args
	 *            should contain the name of an input file.
	 */
	public static void main(String[] args) {
		runFileLoader(new SerializedInstancesLoader(), args);
	}
}
